Ok, thanks for walking me through all the options, I think I have it now. Someone, correct me if I'm wrong:
1) Pack lighter. I cannot bring my large suitcases. My son could barely lift them to get them up a curb. I'm going to go with 3 medium size and if we still need more space, I'll have my kids get those giant backpacks (what else are kids good for if not to carry our stuff? ;) )
2) Get a car from Geneva airport to Interlaken. OR If the cost is outrageous, take a train from the airport to Bern, then Bern to Interlaken. Either way, I will drop some of our luggage off at Interlaken*
*I cannot find any definitive answer on whether they have luggage storage here or just lockers. Ive found a hundred posts over the years from people asking if there is luggage storage there, and everyone just replies with a link to the SBB website. On the website, when you go to Interlaken Ost page and look under services, it just says "Baggage".....no description. I have spent the past couple hours trying to find more specific information, or at least first-hand information, and have come up with nothing. I guess this is one of the great mysteries of Switzerland. If just lockers I guess we can drop some of our smaller bags there? And if larger storage areas, our bigger bags. I will need to find out for sure first so I know what to pack in which bags as obviously I can leave all of our cruise clothes in Interlaken.
3) Interlaken to Lauterbrunnen (with less luggage - yay!)
4) Lauterbrunnen to Wengen
Then when leaving Switzerland:
1) Wengen to Lauterbrunnen
2) Lauterbrunnen to Interlaken Ost. Pick up luggage (More luggage - booo!)
3) Interlaken to Spiez
4) Spiez to Milan
5) Milan to Venice
I can't think about what I will do when I get to Venice right now. I have to get through this part first.
And for the record, I am not disabled, I just have VERY bad back/neck issues which is fine as long as I don't try to lift anything more than a few pounds.